The invention relates to a multiphase electrical gas expansion circuit breaker having a plurality of arc extinguishing chambers arranged parallel to one another side by side in a cubicle with a sealed enclosure filled with a high dielectric strength gas, notably sulphur hexafluoride, the arc extinguishing chamber of each pole comprising:
a closed housing in which a gas pressure rise takes place due to the action of the arc, PA0 a pair of separable aligned stationary and movable contacts extending in the direction of the longitudinal axis of the housing, one at least of said contacts being hollow to ensure communication between the closed housing of each pole and of the enclosure, which forms an expansion volume for the gas extinguishing chamber.
The pole housings located in the common cubicle of a three-phase circuit breaker are generally speaking made of insulating or non-magnetic material. The electric arc developed in one of the poles is subjected to the magnetic induction generated by the neighbouring pole or poles, giving rise to a force tending to displace the arc. This stray effect of the adjacent poles is greater the closer together the poles are. A wide spacing apart of the poles enables this stray effect to be notably reduced, but this increases the overall dimensions of the cubicle.
The influence of the magnetic stray field due to the neighbouring poles is particularly harmful to arc interruption in a gas expansion circuit breaker. The lateral displacement of the arc leads to off-centering of the arc roots in relation to the longitudinal axis of the enclosure. This off-centering affects the gas outflow to the expansion volume of the cubicle, and may hinder the breaking process.
The object of the invention is to achieve a multiphase gas expansion circuit breaker having a cubicle with small dimensions, and which is insensitive to the effect of the proximity of the different poles inside the cubicle.